The teachings of U.S. patent application Ser. No. 10/353,672, filed on Jan. 29, 2003, are herein incorporated by reference.
1. Field of the Invention
The invention relates to an electric screwdriver that can efficiently transmit torque for screw-tightening operation and release the torque transmission.
2. Description of the Related Art
An electric screwdriver is disclosed in unexamined Japanese laid-open patent publication No. 61-219581. The known screwdriver includes a silent clutch mechanism to connect a tool to a motor for transmitting the rotating torque of the motor to the tool. The silent clutch includes clutch members with clutch teeth that can be engaged with each other to transmit the motor torque to the tool. By utilizing the silent clutch mechanism, when the screw is tightened to a predetermined depth with respect to the workpiece, the clutch members can be promptly disengaged to stop transmission of the rotating torque of the driving motor. As a result, noise and vibration during screw-tightening operation can be avoided.
In the known screwdriver, the silent clutch mechanism is disposed between a rotating member on the motor side and a rotating member on the tool side. In order to transmit the rotating torque of the motor to the tool, user of the screwdriver applies a pressing load on the screwdriver while keeping the tool in abutment on the workpiece. At this time, the tool side rotating member moves toward the motor side rotating member and engages it. As a result, the motor torque is transmitted to the tool via the both rotating members which have been engaged with each other.
In the above-mentioned known technique, in order to transmit the motor torque to the tool, the user must apply a pressing load on the screwdriver to keep torque transmission from the motor to the tool via the mutually engaged rotating members. Otherwise, the torque transmission is cancelled when the pressing load of the user is not applied onto the screwdriver. However, as for a screw such as a universal joint, which is tightened in a relatively narrow work area, the user of the known screwdriver may be in difficulty to continuously apply a pressing load onto the screwdriver during the screw tightening operation.